The present invention is directed to ink compositions. More specifically, the present invention is directed to ink compositions particularly suitably for thermal ink jet printing. One embodiment of the present invention is directed to an ink composition which comprises water, a dye, and a compound selected from the group consisting of N,N'-bis(3-aminopropyl)-1,2-ethylenediamine, 1,4-bis(3-aminopropyl)piperazine, N,N'-bis(3-aminopropyl)-1,3-propanediamine, N,N'-bis(2-aminoethyl)-1,3-propanediamine, N,N'-bis(3-aminopropyl)-1,4-butanediamine, ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, nitrilotrisethylamine, N,N'-(diaminoethyl)piperazine, piperazinylethylethylenediamine, aminoethyltriethylenetetramine, aminoethylpiperazinylethylethylenediamine, pentaethylene hexamine, piperazinylethyldiethylenetriamine, and mixtures thereof, said ink composition having a pH of more than about 8 and less than about 9. Another embodiment of the present invention is directed to an ink composition which comprises water, a dye, a polyamine compound, and a monoamine compound of the formula ##STR2## wherein R.sup.1, R.sup.2, and R.sup.3 are independently selected from the group consisting of hydrogen, alkyl, and substituted alkyl. Yet another embodiment of the present invention is directed to an ink composition which comprises water, a dye, a first generation dendrimer compound having terminal primary amine groups, and a monoamine compound of the formula ##STR3## wherein R.sup.1, R.sup.2, and R.sup.3 are independently selected from the group consisting of hydrogen, alkyl, and substituted alkyl. Ink compositions of the present invention exhibit improved waterfastness and other advantages as set forth herein.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. Nos. 4,601,777, 4,251,824, 4,410,899, 4,412,224, and 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Ink compositions for ink jet printing are known. For example, U.S. Pat. No. 4,155,768 (Adams et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink for use in ink jet printers which contains a water soluble dye and a polyamine containing 6 or fewer nitrogen atoms per molecule, with the ink having a pH of 8 or below. The ink has improved waterfastness over an equivalent ink formulation without the polyamine additive.
U.S. Pat. No. 4,197,135 (Bailey et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink for use in ink jet printers which contains a water soluble dye and a polyamine containing 7 or more nitrogen atoms per molecule, with the ink composition having a pH of 8 or above. The ink has improved waterfastness over an equivalent ink formation without the polyamine additive.
U.S. Pat. No. 5,100,470 (Hindagolla et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink jet ink comprising a water soluble dye, water with or without a water soluble organic solvent, and sufficient polyalkylene polyamine to provide the ink with a pH of at least 9. About 2 to 10 percent urea may be added to the ink to reduce crusting of the ink.
U.S. Pat. No. 5,098,475 (Winnik et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition comprising a solution with a dendrimer colored with a dye or dyes covalently attached thereto. As optional additives there may be included in the ink humectants and biocides. The inks can be prepared by mixing the appropriate components such as a dendrimer, water, and a reactive dye. Also disclosed is a process for the utilization of the aforementioned compositions and ink jet printing processes.
U.S. Pat. No. 5,120,361 (Winnik et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition comprising a solution which comprises a dendrimer and a dye or dyes.
U.S. Pat. No. 5,108,503 (Hindagolla et al.) discloses inks for ink jet printing which have improved water resistance and smear resistance, containing from about 2.5 to about 25 percent by weight, preferably from about 7.5 to about 12.5 percent by weight of 2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone, or mixtures thereof.
Although known compositions and processes are suitable for their intended purposes, a need remains for improved ink compositions suitable for use in thermal ink jet printing processes. In addition, there is a need for ink compositions for use in thermal ink jet printing processes which exhibit improved waterfastness. Further, a need remains for ink compositions suitable for generating waterfast images in thermal ink jet printing processes which are nontoxic and nonmutagenic.